Bilateral extra-adrenal perirenal myelolipoma associated with obstructive uropathy

A 58-year-old man with hypertension and diabetes mellitus complicated by diabetic nephropathy presented with a right flank pain. The patient denied urinary complaints, gross hematuria, fever, or chills. There was no history of nephrolithiasis. Laboratory studies revealed significant worsening of kidney function (on admission, creatinine was 5.9 mg/dl, while baseline creatinine was 3.1 mg/dL). On computed tomography (CT), bilateral large fat density masses were noted around the perirenal spaces, which encompassed and compressed both kidneys. Mild to moderate hydronephrosis and dilatation of the right collecting system was also noted (Fig. 1 A and B, white arrows). A percutaneous biopsy from the perirenal mass revealed mature adipose tissue interspersed with hematopoietic precursors (Fig. 2A, Hematoxylin and eosin stain). Immunohistochemical staining was positive for CD71 confirmed the presence of erythroid cells (Fig. 2B). These findings were compatible with a diagnosis of perirenal myelolipoma. Given his clinical presentation and imaging findings, obstruction by the perirenal mass was suspected and double J stent was inserted, resulting in improvement of kidney function, and return to baseline creatinine value. Myelolipoma are uncommon mesenchymal tumor composed of adipose tissue and hematopoietic cells. The most common location of myelolipoma is the adrenal gland. Perirenal extra-adrenal myelolipoma are scarce, and only few cases have been reported to date. ^{,  ,}  Although the precise etiology of these tumors is not known, several hypotheses have been suggested, including adrenal cortical cells metaplasia, misplacement of myeloid cells during embryogenesis and embolization of bone marrow. Myelolipoma should be differentiated from other fat-containing lesions, particularly liposarcoma. Despite the benign nature of myelolipoma, large mass may occasionally undergo necrosis and hemorrhage, as well as compress surrounding structures. In our case, the large mass caused obstruction accompanied by deterioration of kidney function, relieved by inserting stent in the ureter.